1. Field of the Invention
The present invention relates to a plasma processing apparatus and to an evaluation method, a performance management system, and a performance validation system for the plasma processing apparatus and a plasma processing system. More particularly, the present invention is suitable for continuously securing the performance of the plasma processing apparatus to be maintained at a required level even after the plasma processing apparatus or system is delivered to a customer site.
2. Description of the Related Art
FIG. 22 illustrates an example of a conventional dual-frequency excitation plasma processing apparatus which performs a plasma process such as a chemical vapor deposition (CVD) process, a sputtering process, a dry etching process, or an ashing process.
In the plasma processing apparatus shown in FIG. 22, a matching circuit 2A is inserted between a radiofrequency generator 1 and a plasma excitation electrode 4. The matching circuit 2A serves as a circuit that matches the impedance between the radiofrequency generator 1 and the excitation electrode 4.
Radiofrequency power from the radiofrequency generator 1 is fed to the plasma excitation electrode 4 via the matching circuit 2A and a feed plate 3. The matching circuit 2A is accommodated in a matching box 2 which is a housing composed of a conductive material. The plasma excitation electrode 4 and the feed plate 3 are covered by a chassis 21 made of a conductor.
The plasma excitation electrode 4 is provided with a projection 4a at the lower side thereof. A shower plate 5 having many holes 7 provided under the plasma excitation electrode 4 is in contact with the projection 4a. The plasma excitation electrode 4 and the shower plate 5 define a space 6. A gas feeding tube 17 comprising a conductor is connected to the space 6. The gas feeding tube 17 is provided with an insulator 17a at the middle thereof so as to insulate the plasma excitation electrode 4 and the gas source.
Gas from the gas feeding tube 17 is fed inside a chamber space 60 composed of a chamber wall 10, via the holes 7 in the shower plate 5. An insulator 9 is disposed between the chamber wall 10 and the plasma excitation electrode 4 (cathode) to provide insulation therebetween. The exhaust system is omitted from the drawing.
A wafer susceptor (susceptor electrode) 8 which receives a substrate 16 and also serves as a plasma excitation electrode is installed inside the chamber space 60. A susceptor shield 12 is disposed under the wafer susceptor 8.
The susceptor shield 12 comprises a shield supporting plate 12A for receiving the susceptor electrode 8 and a cylindrical supporting cylinder 12B extending downward from the center of the shield supporting plate 12A. The supporting cylinder 12B penetrates a chamber bottom 10A, and the lower portion of the supporting cylinder 12B and the chamber bottom 10A are hermetically sealed with bellows 11.
The shaft 13 and the susceptor electrode 8 are electrically isolated from the susceptor shield 12 by a gap between the susceptor shield 12 and the susceptor electrode 8 and by insulators 12C provided around the shaft 13. The insulators 12C also serve to maintain high vacuum in the chamber space 60. The susceptor electrode 8 and the susceptor shield 12 can be moved upward and downward by the bellows 11 in order to control the distance between plasma excitation electrodes 4 and 8.
The susceptor electrode 8 is connected to a second radiofrequency generator 15 via the shaft 13 and a matching circuit accommodated in a matching box 14. The chamber wall 10 and the susceptor shield 12 have equal DC potentials.
FIG. 23 illustrates another example of a conventional plasma processing apparatus. Unlike the plasma processing apparatus shown in FIG. 22, the plasma processing apparatus shown in FIG. 23 is of a single-frequency excitation type. In other words, a radiofrequency power is supplied only to the cathode electrode 4 and the susceptor electrode 8 is grounded. Moreover, the matching box 14 and the radiofrequency generator 15 shown in FIG. 18 are not provided. The susceptor electrode 8 and the chamber wall 10 have the same DC potential.
In these plasma processing apparatuses, power with a frequency of approximately 13.56 MHz is generally supplied in order to generate a plasma between the electrodes 4 and 8. A plasma process such as a plasma-enhanced CVD process, a sputtering process, a dry etching process, or an ashing process is then performed using the plasma.
The operation validation and the evaluation of the above-described plasma processing apparatuses have been conducted by actually performing the process such as deposition and then evaluating the deposition characteristics thereof as follows.
(1) Deposition Tate and In-plane Uniformity
The process of determining and evaluating deposition rates and planar uniformity includes the following.
Step 1: Depositing a desired layer on a 6-inch substrate by a plasma-enhanced CVD process.
Step 2: Patterning a resist layer.
Step 3: Dry-etching the layer.
Step 4: Separating the resist layer by ashing.
Step 5: Measuring step differences in the layer thickness using a contact-type displacement meter.
Step 6: Calculating the deposition rate from the deposition time and the layer thickness.
Step 7: Measuring the in-plane uniformity at 16 points.
(2) BHF Etching Rate
The process of determining etching rates includes the following.
A resist mask is patterned as in Steps 1 and 2 above.
Step 3: Immersing the substrate in a buffered hydrofluoric acid (BHF) solution for one minute.
Step 4: Rinsing the substrate with deionized water, drying the substrate, and separating the resist mask using a mixture of sulfuric acid and hydrogen peroxide (H2SO4+H2O2)
Step 5: Measuring the step difference as in Step 5 above.
Step 6: Calculating the etching rate from the immersion time and the step differences.
(3) Isolation Voltage
The process of determining and evaluating the isolation voltage includes the following.
Step 1: Depositing a conductive layer on a glass substrate by a sputtering method and patterning the conductive layer to form a lower electrode.
Step 2: Depositing an insulation layer by a plasma-enhanced CVD method.
Step 3: Forming an upper electrode as in Step 1.
Step 4: Forming a contact hole for the lower electrode.
Step 5: Measuring the current-voltage characteristics (I–V characteristics) of the upper and lower electrodes by using probes while applying a voltage of approximately 200 V or less.
Step 6: Defining the isolation voltage as the voltage V at 100 pA corresponding 1 μA/cm2 in a 100 μm square electrode.
The plasma processing apparatus has been required to achieve a higher plasma processing rate (the deposition rate or the processing speed), increased productivity, and uniformity of the plasma processing in the in-plane direction of the substrates to be treated (uniformity in the distribution of the layer thickness in the in-plane direction and uniformity in the distribution of the process variation in the in-plane direction). As the size of substrates has been increasing in recent years, the requirement for uniformity in the in-plane direction is becoming tighter.
Moreover, as the size of the substrate is increased, the power required is also increased to the order of kilowatts, thus increasing the power consumption. Accordingly, as the capacity of the power supply increases, both the cost for developing the power supply and the power consumption during the operation of the apparatus are increased. In this respect, it is desirable to reduce the operation costs.
Furthermore, an increase in power consumption leads to an increase in emission of carbon dioxide which places a burden on the environment. Since the power consumption is increased by the combination of increase in the size of substrates and a low power consumption efficiency, there is a growing demand to reduce the carbon dioxide emission.
The density of the plasma generated can be improved by increasing the plasma excitation frequency. For example, a frequency in the VHF band of 30 MHz or more can be used instead of the conventional 13.56 MHz. Thus, one possible way to improve the deposition rate of a deposition apparatus such as a plasma-enhanced CVD apparatus is to employ a high plasma excitation frequency.
Another type of plasma processing apparatus is one having a plurality of plasma chambers (multi-chamber plasma processing apparatus). Such a plasma processing apparatus is also required to achieve a higher plasma processing rate (the deposition rate or the processing speed), increased productivity, and uniformity of the plasma processing in the in-plane direction of the substrates (uniformity in the distribution of the layer thickness in the in-plane direction and uniformity in the distribution of the process variation in the in-plane direction), even when the substrates are treated in different plasma chambers. There is also a demand to eliminate operational differences among the plurality of the plasma chambers, thus avoiding processing variations.
Moreover, the respective plasma chambers of the plasma processing apparatus having the plurality of plasma processing chambers are required to achieve substantially the same plasma processing results by using the same process recipe specifying external parameters such as the flow and pressure of the charged gasses, power supply, and treatment time.
At the time of initial installation or maintenance of the plasma processing apparatus, there is a demand to reduce the amount of time required for adjusting the apparatus to eliminate differences among the plural plasma chambers and processing variations, so that substantially the same process results can be achieved by using the same process recipe. Reduction of the cost required for such an adjustment is also required.
Furthermore, a plasma processing system equipped with a plurality of the above-described plasma processing apparatuses is also required to eliminate plasma processing variations among individual plasma chambers of the individual plasma processing apparatuses.
In the above-described conventional plasma processing apparatuses, the power consumption efficiency (the ratio of the power consumed in the plasma processing chamber to the power supplied from the radiofrequency generator 1 to the plasma excitation electrode 4) is not satisfactory. Especially as the frequency supplied from the radiofrequency generator is increased, the power consumption efficiency in the plasma processing apparatus becomes significantly lower. Moreover, the power consumption efficiency decreases as the substrate size becomes larger.
As a result, the effective power consumed in the plasma space is low due to the low power consumption efficiency, resulting in a lower deposition rate. Moreover, when applied to the deposition of insulating layers, it is difficult to form insulating layers of high isolation voltage.
While the plasma processing apparatus is required to achieve a desired performance level, the multi-chamber plasma processing apparatus having the plurality of plasma processing chambers and the plasma processing system are required to eliminate the differences in the performance of plasma process among the plurality of plasma processing chambers. Even when the plasma processing apparatus is optimized as above, the level of the performance may not be maintained at the desired level and the differences among the plasma processing chambers may occur after the plasma processing apparatus has repeated plasma processes. When adjustment works such as overhauling, parts replacement, assembly with alignment or the like are performed, it is possible that the performance is not maintained at the level maintained before the adjustment works. When the plasma processing apparatus is transferred, the plasma processing apparatus is disassembled first, transferred, and then reassembled at the customer site. In this case also it is possible that the performance is not maintained at the level maintained before the transfer due to the vibration during the transfer and inappropriate reassembly work.
When processes (1) to (3) described above are employed to evaluate whether the operation of the plasma processing apparatus and the difference among the plasma processing chambers are maintained within the required levels, it becomes necessary to actually operate the plasma processing apparatus and to examine the treated substrates using an ex-situ inspection method requiring a plurality of steps.
Such an evaluation takes several days to several weeks to yield evaluation results, and the characteristics of the substrates manufactured during that period, assuming that the manufacturing line is not stopped, remain unknown during that period. If the status of the plasma processing apparatus is not satisfactory, the resulting products will not meet predetermined standards. In this respect, a method that facilitates maintenance of the plasma processing apparatus has been demanded.
The conventional plasma processing apparatuses described above are designed to use a power having a frequency of approximately 13.56 MHz and is not suited for higher frequencies. To be more specific, the units to which the radiofrequency voltage is delivered, i.e., the chambers in which plasma processing is performed, are designed without taking into an account radiofrequency characteristics such as impedance and resonance frequency characteristics and thus have the following problems.
First, when a power having a frequency exceeding 13.56 MHz is delivered, no improvement is achieved in the deposition rate during the deposition process, but rather the deposition rate is decreased in some cases.
Second, although the density of a generated plasma increases as the frequency increases, the density starts to decrease once its peak value is reached, eventually reaching a level at which glow-discharge is no longer possible, thus rendering further increases in frequency pointless.
In addition to the disadvantages described above, the conventional plasma processing apparatuses have the following disadvantages.
The conventional multi-chamber type plasma processing apparatus and plasma processing system, both comprising a plurality of plasma chambers, are not designed to eliminate the differences in electrical radiofrequency characteristics such as impedance and resonant frequency characteristics among the plasma chambers. Thus, it is possible that the effective power consumed in each of plasma spaces and the density of the generated plasma differ between each of the plasma chambers.
Also, the same plasma processing results may not be obtained even when the same process recipe is applied to these plasma chambers.
Accordingly, in order to obtain the same plasma processing results, external parameters such as gas flow/pressure, power supply, process time, and the like must be compared with the process results according to evaluation methods (1) to (3) described above for each of the plasma chambers so as to determine the correlation between them. However, the amount of data is enormous and it is impossible to completely carry out the comparison.
When methods (1) to (3) described above are employed to validate and evaluate the operation of the plasma processing apparatus, it becomes necessary to actually operate the plasma processing apparatus and to examine the treated substrates using an ex-situ inspection method comprising a plurality of steps.
Since such an inspection requires several days to several weeks to yield evaluation results, it is desired that the time required for performance inspection of a plasma processing apparatus be reduced especially when the apparatus is in the development stage.
Moreover, when methods (1) to (3) described above are employed to inspect the plasma processing apparatus or system having a plurality of plasma chambers, the time required for adjusting the plasma processing chambers so as to eliminate the difference in performance and variation in processing among the plasma processing chambers to achieve the same processing results using the same process recipe may be months. The time required for such adjustment needs to be reduced. Also, the cost of substrates for inspection, the cost of processing the substrates for inspection, the labor cost for workers involved with the adjustment, and so forth are significantly high.
As described above, while the plasma processing apparatus is required to achieve a desired performance level, the multi-chamber plasma processing apparatus having the plurality of plasma processing chambers and the plasma processing system are required to eliminate the differences in the performance of plasma process among the plurality of plasma processing chambers.
Even when the plasma processing apparatus has been optimized as above, the plasma processing apparatus is generally disassembled before the transfer and then reassembled at the customer site. Thus, it is possible that the performance is not maintained at the level generated before the transfer due to the vibration during the transfer and inappropriate reassembly work.
When processes (1) to (3) described above are employed to evaluate whether the operation of the plasma processing apparatus and the difference among the plasma processing chambers are maintained within the required levels, it becomes necessary to actually operate the plasma processing apparatus and to examine the treated substrates using an ex-situ inspection method requiring a plurality of steps.
If the performance of the plasma processing apparatus does not satisfy the required levels, it is necessary to repeat long series of cycles of adjusting the plasma processing apparatus, performing a plasma process on a substrate, and evaluating the processed substrate, thereby extending the initialization process of the delivered plasma processing apparatus. The length of the time required to complete the initialization process of a production line directly effects the annual sales, and a prolonged initialization process leads to an opportunity loss since the products can not be made available for the market at a suitable time.
Thus, it is desired that the validation of the performance of the plasma processing apparatus be performed more easily and that the cycle of fault detection and performance of corrective action be performed in a shorter period of time, so as to shorten the initialization process of the plasma processing apparatus.